PhoneBlox-style fancy modular smartphones are an interesting prospect, but I really wish there was a simple replaceable-parts phone design based on ordinary development-board-style PCBs. Make it about 25mm thick and then it would be somewhat viable to carry around as a nerdy but genuinely usable phone, while still having enough internal space to be based on replaceable PCBs without too much pressure to miniaturise. Such a standard would have lots of utility: as a testbed for commercial phone development, as a place to experiment with new hardware or software for phones, as a phone (or just a gadget) incorporating niche (or "niche-of-one") hardware or software you can't get in a commercial device, as the equivalent of a self-build PC for enthusiasts.